Semiconductor devices and methods for manufacturing the same

ABSTRACT

Provided are semiconductor devices and methods for manufacturing the same. An example method may include: forming a first semiconductor layer and a second semiconductor layer sequentially on a substrate; patterning the second semiconductor layer and the first semiconductor layer to form a fin; forming an isolation layer on the substrate, wherein the isolation layer exposes a portion of the first semiconductor layer; implanting ions into a portion of the substrate beneath the fin, to form a punch-through stopper; forming a gate stack crossing over the fin on the isolation layer; selectively etching the second semiconductor layer with the gate stack as a mask, to expose the first semiconductor layer; selectively etching the first semiconductor layer, to form a void beneath the second semiconductor layer; and forming a third semiconductor layer on the substrate, to form source/drain regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application of PCT ApplicationNo. PCT/CN2012/085817, filed on Dec. 4, 2012, entitled “SemiconductorDevices and Methods for Manufacturing the Same,” which claims priorityto Chinese Patent Application No. 201210448686.1, filed on Nov. 9, 2012.Both the PCT Application and the Chinese Application are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the semiconductor technology, andparticularly to semiconductor devices and methods for manufacturing thesame.

BACKGROUND

Short channel effects are getting more significant as planarsemiconductor devices are increasingly being scaled down. To this end,three-dimensional (3D) semiconductor devices, such as Fin Field EffectTransistors (FinFETs), have been proposed. Generally, a FinFET includesa fin formed vertically on a substrate and a gate stack intersecting thefin. In addition, an isolation layer is formed on the substrate toisolate the gate stack from the substrate. As such, the fin has itsbottom surrounded by the isolation layer. Therefore, it is difficult forthe gate to effectively control the bottom of the fin. As a result, aleakage current tends to occur between a source and a drain via thebottom of the fin.

SUMMARY OF THE DISCLOSURE

The present disclosure aims to provide, among others, semiconductordevices and methods for manufacturing the same.

According to an aspect of the present disclosure, a method formanufacturing a semiconductor device is provided, comprising: forming afirst semiconductor layer and a second semiconductor layer sequentiallyon a substrate; patterning the second semiconductor layer and the firstsemiconductor layer to form a fin; forming an isolation layer on thesubstrate, wherein the isolation layer exposes a portion of the firstsemiconductor layer; implanting ions into a portion of the substratebeneath the fin, to form a punch-through stopper; forming a gate stackcrossing over the fin on the isolation layer; selectively etching thesecond semiconductor layer with the gate stack as a mask, to expose thefirst semiconductor layer; selectively etching the first semiconductorlayer, to form a void beneath the second semiconductor layer; andforming a third semiconductor layer on the substrate, to formsource/drain regions.

According to another aspect of the present disclosure, a semiconductordevice is provided, comprising: a fin formed on a substrate; apunch-through stopper formed in the substrate beneath the fin; anisolation layer formed on the substrate; and a gate stack formed on theisolation layer and crossing over the fin, wherein the fin comprises aportion composed of a first semiconductor layer beneath the gate stackand a portion composed of a second semiconductor layer abutting thefirst semiconductor layer, and wherein the semiconductor device furthercomprises source/drain regions formed in the portion composed of thesecond semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentdisclosure will become apparent from following descriptions ofembodiments with reference to the attached drawings, in which:

FIGS. 1 to 18 are schematic diagrams showing a flow for manufacturing asemiconductor device according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Hereinafter, the technology disclosed herein is described with referenceto embodiments thereof shown in the attached drawings. However, itshould be noted that those descriptions are just provided forillustrative purpose, rather than limiting the present disclosure.Further, in the following, descriptions of known structures andtechniques are omitted so as not to obscure the concept of the presentdisclosure.

In the drawings, various structures according to the embodiments areschematically shown. However, they are not drawn to scale, and somefeatures may be enlarged while some features may be omitted for sake ofclarity. Moreover, shapes and relative sizes and positions of regionsand layers shown in the drawings are also illustrative, and deviationsmay occur due to manufacture tolerances or technique limitations inpractice. Those skilled in the art can also devise regions/layers ofother different shapes, sizes, and relative positions as desired.

In the context of the present disclosure, when a layer/element isrecited as being “on” a further layer/element, the layer/element can bedisposed directly on the further layer/element, or otherwise there maybe an intervening layer/element interposed therebetween. Further, if alayer/element is “on” a further layer/element in an orientation, thenthe layer/element can be “under” the further layer/element when theorientation is turned.

According to an embodiment of the present disclosure, a relatively highthreshold voltage region may be formed in a substrate beneath a fin, toreduce the source/drain leakage. In an example, the relatively highthreshold voltage region may include a relatively highly-doped region,or a punch-through stopper. The punch-through stopper may be formed byimplanting ions into the substrate beneath the fin after the fin isformed. For example, p-type implantation may be performed for an n-typedevice; or n-type implantation may be performed for a p-type device.

Due to the ion implantation, a relatively high dopant concentration mayexist in the fin (especially in the bottom of the fin close to the ionimplanted region). This in turn results in great random dopingfluctuation in the fin, thereby degrading device performances. Accordingto an embodiment of the present disclosure, the fin may be formed insuch way that the fin includes a stack of a sacrificial layer and a finbody layer, wherein the sacrificial layer is located at the bottom ofthe fin. After the ion implantation for forming the punch-throughstopper, the sacrificial layer, which is potentially contaminated by theion implantation, may be selectively removed. Therefore, the randomdoping fluctuation in the fin may be reduced, thereby further improvingthe device performances.

According to another embodiment of the present disclosure, to furtherreduce the source/drain leakage, after the sacrificial layer is removedas described above, an isolation island may be formed between a sourceand a drain at the bottom of the fin, to reduce a leakage currentbetween the source and the drain via the bottom of the fin. For example,after the sacrificial layer is removed, a dielectric material may befilled beneath the fin body layer and patterned into an isolationisland.

As it is desirable to locate the isolation island between the source andthe drain, a gate stack may be used as a mask in patterning theisolation island. Specifically, after the sacrificial layer and the finbody layer are patterned into a fin, an isolation layer may be formed onthe substrate and a (sacrificial) gate stack crossing over the fin mayformed on the isolation layer. The isolation layer exposes a portion ofthe sacrificial layer, because the isolation layer defines the “bottom”of the fin. Then, the fin body layer may be selectively etched with the(sacrificial) gate stack as a mask (thereby leaving the fin body layerbeneath the gate stack), to expose the sacrificial layer. Next, thesacrificial layer may be selectively etched to remove the sacrificiallayer (for example, the sacrificial layer may be removed completely). Assuch, a void is formed beneath the fin body layer. Next, a dielectricmaterial may be deposited and etched back (with the gate stack as amask), so that the void beneath the fin body layer is filled with thedielectric material to form an isolation island.

On the other hand, after the sacrificial layer is removed as describedabove, an opening having a shape corresponding to that of the fin isformed in the isolation layer and exposes a portion of the substrate.Then, source/drain regions may be formed on the substrate through theopening by, for example, epitaxy.

According to another embodiment of the present disclosure, the formedsource/drain regions may comprise a semiconductor material differentfrom that of the fin body layer, and thus can apply stress to the fmbody layer (in which a channel region is to be formed) due to mismatchof lattices between the source/drain regions and the fin body layer,thereby further improving the device performances.

According to an embodiment of the present disclosure, the isolationlayer may be formed by depositing a dielectric material on the substrateand then etching it back. The dielectric material may be formed in suchway that when the dielectric material substantially covers the fin(i.e., in case of multiple fins, substantially fills up gaps between thefins), a portion of the dielectric material on top of the fin may have athickness sufficiently less than that of a portion of the dielectricmaterial on the substrate. For example, the portion of the dielectricmaterial on top of the fin may have a thickness less than ⅓, preferably¼, of the thickness of the portion of the dielectric material on thesubstrate. This may be implemented by, for example, High Density Plasma(HDP) deposition. In case of forming a plurality of fins, a portion ofthe dielectric material on top of each of the fins may have a thicknessless than half of a spacing between the fin and its neighboring fin. Assuch, an etching depth may be reduced in the subsequent etching-backprocess, and thus accuracy for controlling the etching may be improved.

The present disclosure may be presented in various forms, and someexamples thereof will be described hereafter.

As shown in FIG. 1, a substrate 1000 is provided. The substrate 1000 maycomprise any substrate in various forms, for example, but not limitedto, bulk semiconductor substrate such as bulk Si substrate,Semiconductor On Insulator (SOI) substrate, SiGe substrate and the like.In the following, a bulk Si substrate is described by way of example forconvenience of description.

An n-type well 1000-1 and a p-type well 1000-2 may be formed in thesubstrate 1000, so that a p-type device and an n-type device may beformed later therein, respectively. For example, the n-type well 1000-1may be formed by implanting n-type dopants (such as P or As) into thesubstrate 1000, and the p-type well 1000-2 may be formed by implantingp-type dopants (such as B) into the substrate 1000. If required,annealing may be performed after the implantation. To those skilled inthe art, the n-type and p-type wells may be formed in various methods,and detailed descriptions thereof will be omitted here.

It is to be noted that a process of forming complementary devices in therespective n-type and p-type wells will be described below, but thepresent disclosure is not limited thereto. The present disclosure isalso applicable to a non-complementary process, for example. Further,some of the following processes related to the complementary devices maynot be necessary in some implementations.

A first semiconductor layer 1002 may be formed on the substrate 1000 by,for example, epitaxy. In an example, the first semiconductor layer 1002may comprise SiGe (wherein Ge may have an atomic percentage of about5-20%), with a thickness of about 10-50 nm. Next, a second semiconductorlayer 1004 may be formed by, for example, epitaxy on the firstsemiconductor layer 1002. In an example, the second semiconductor layer1004 may comprise Si with a thickness of about 20-100 nm.

In an example of the present disclosure, a protection layer 1006 may beformed on the second semiconductor layer 1004. For example, theprotection layer 1006 may comprise oxide (for example, silicon oxide)with a thickness of about 10-50 nm. Such a protection layer 1006 canprotect end portions of fins in subsequent processes.

The formed second semiconductor layer 1004, first semiconductor layer1002, and substrate may be then patterned to form the fins. For example,this can be done as follows. In particular, photoresist 1008 may beformed and then patterned as designed on the protection layer 1006. Thephotoresist 1008 is generally patterned into a series of parallelequispaced lines. Then, as shown in FIG. 2, the protection layer 1006,the second semiconductor layer 1004, the first semiconductor layer 1002and the substrate 1000 may be sequentially selectively etched by, forexample, Reactive Ion Etching (RIE), with the patterned photoresist 1008as a mask, thereby forming the fins.

In case of the complementary process, an isolation may be formed betweenthe n-type and p-type regions as shown in FIG. 3. In particular,photoresist 1010 may be formed on the substrate, and then patterned toexpose a region around an interface between the n-type and p-typeregions. Then, portions of the protection layer and the second and firstsemiconductor layers existing in this region are selectively etched by,for example, RIE. The substrate may be further selectively etched by,for example, RIE. As such, an isolation zone is formed between then-type and p-type regions, and may subsequently be filled withdielectric. Then, the photoresist 1010 may be removed.

It can be seen that in the process of FIG. 2, the etching for formingthe fins is performed into the substrate 1000. Then, with the process ofFIG. 3, a contact area between the p-type and n-type wells (i.e., anarea of a resultant pn junction) may be made small. However, the presentdisclosure is not limited thereto. For example, in the non-complementaryprocess or in a local region of devices of a single type (p-type orn-type), the etching of the first semiconductor layer 1002 as describedabove in conjunction with FIG. 2 may stop on the substrate 1000, and itis not necessary to further etch the substrate 1000; and the process ofFIG. 3 may be performed but may not be necessary. Trenches (between thefins) formed by the etching may have a shape different from the regularrectangular shape as shown in FIG. 2, such as a tapered shape narrowedfrom top down. In addition, the positions and number of the formed finsare not limited to the example as shown in FIG. 2.

In the example of FIG. 2, a fin is also formed at the interface betweenthe n-type well 1000-1 and the p-type well 1000-2. The fin is thenremoved by the isolation forming process of FIG. 3, resulting in thestructure shown in FIG. 4.

After the fins are formed in the above process, gate stacks crossingover the respective fins may be formed to achieve final semiconductordevices.

To isolate the gate stacks from the substrate, an isolation layer may beformed on the substrate. This isolation layer may be formed by, forexample, depositing a dielectric material on the substrate, and thenetching it back. In addition, in the etching-back process, an etchingdepth may be controlled so that the etched isolation layer exposes aportion of the first semiconductor layer (for example, a top surface ofthe isolation layer may be located between a top surface and a bottomsurface of the first semiconductor layer). In an example, the isolationlayer may comprise High Density Plasma (HDP) oxide, such as siliconoxide.

To improve uniformity in level of (the top surface of) the isolationlayer after being etched back, and thus improve uniformity in height offinally-formed fins, the dielectric material 1014 may be deposited insuch a way that it substantially covers the fins (i.e., in case ofmultiple fins, substantially fills up gaps between the fins), as shownin FIG. 5. According to embodiments of the present disclosure, thedielectric material may be deposited such that a portion of thedielectric material on top of the fins has a thickness sufficiently lessthan that of a portion of the dielectric material on the substrate. Ingeneral, the thickness of the portion of the dielectric material on topof the fins is less than ⅓, preferably ¼, of the thickness of theportion of the dielectric material on the substrate. In an example, theportion of the dielectric material on top of each of the fins may have athickness no more than 20 nm, and the portion of the dielectric materialon the substrate may have a thickness up to about 100 nm.

According to an example of the present disclosure, the dielectricmaterial 1014 may comprise oxide (e.g., silicon oxide) formed by HighDensity Plasma (HDP) deposition. Due to characteristics of HDP, thethickness of the dielectric material on top of the fins (in a directionperpendicular to the substrate) and on side surfaces of the fins (in adirection parallel to the substrate, i.e., a lateral direction) is lessthan that of the dielectric material between the fins on the substrate(in a direction perpendicular to the substrate) during the deposition.Due to such characteristics, the HDP deposition is conventionally notused to make oxide isolation.

Here, for example, by controlling deposition conditions, the thicknessof the portion of the dielectric material 1014 on top of each of thefins may be less than ½ of a spacing between the fin and its neighboringfin when the dielectric material 1014 substantially covers the fins(i.e., substantially fills up the gaps between the fins). If spacingsbetween the fins are not the same, the thickness of the portion of thedielectric material 1014 on top of each of the fins may be less than ½of a narrower one of the spacings between the fin and its neighboringfins.

Next, the dielectric material 1014 is etched back as shown in FIG. 6. Asthe etching-back of the dielectric material 1014 is performed with arelatively small depth, it is easy to control the etching, and it isthus possible to more accurately control a distance from the top surfaceof the fin (in this example, the top surface of the second semiconductorlayer 1004) to the top surface of the isolation layer 1014 (whichdetermines at least partially a fin height of the final device and thusa channel width of the final device), so that the distance is keptsubstantially constant across the substrate.

In an example, the protection layer 1006 and the dielectric material1014 comprise the same material, such as oxide. Therefore, in theprocess of etching back the dielectric material 1014, the protectionlayer 1016 may be removed at the same time, as shown in FIG. 6.

To improve the device performances, a punch-through stopper 1038 may beformed in the substrate beneath the fin. Specifically, as shown in FIG.7, the n-type well 1000-1. may be covered with photoresist 1012-1, andthen ion implantation may be performed. Implanted ions will diffuse intoa portion of the substrate surrounded by the isolation layer 1014 viathe isolation layer 1014. For the n-type device to be formed in thep-type well 1000-2, p-type dopants such as B, BF₂, or In may beimplanted. The implantation may be performed at a peak concentration ofabout 1E18-2E19 cm⁻³, for example. The implanted dopants may beactivated through annealing. Then, the photoresist 1012-1 may beremoved.

Similarly, as shown in FIG. 8, the p-type well 1000-2 may be coveredwith photoresist 1012-2, and then (angled) ion implantation may beperformed. For the p-type device to be formed in the n-type well 1000-1,n-type dopants such as As or Sb may be implanted. The implantation maybe performed at a peak concentration of about 1E18-2E19 cm⁻³, forexample. The implanted dopants may be activated through annealing. Then,the photoresist 1012-2 may be removed.

Although the punch-through stopper 1038 is shown in FIGS. 7 and 8 to belocated only in the substrate 1000, it may extend into the firstsemiconductor layer 1002 in practice.

Then, sacrificial gate stacks crossing over the respective fins may beformed on the isolation layer 1014. For example, this may be done asfollows.

In particular, as shown in FIG. 9 (FIG. 9(b) illustrates across-sectional view along line BB′ in FIG. 9(a)), a sacrificial gatedielectric layer 1016 may be formed through, for example, deposition.The sacrificial gate dielectric layer 1016 may comprise, for example,oxide with a thickness of about 0.8-1.5 nm. Although the sacrificialgate dielectric layer 1016 is shown in FIG. 9 as a shape of “Π,” thesacrificial gate dielectric layer 1016 may also include a portionextending onto the top surface of the isolation layer 1014. Then, asacrificial gate conductor layer 1018 may be formed by, for example,deposition. The sacrificial gate conductor layer 1018 may comprise, forexample, polysilicon. The sacrificial gate conductor layer 1018 may fillup the gaps between the fins, and may be planarized by, for example,Chemical Mechanical Polishing (CMP). Next, the sacrificial gateconductor layer 1018 is patterned to form the gate stacks. Thesacrificial gate conductor layer 1018 is patterned into stripsintersecting the respective fins in the example of FIG. 9. In anotherembodiment, the sacrificial gate dielectric layer 1016 may be furtherpatterned with the patterned sacrificial gate conductor layer 1018 as amask.

Next, as shown in FIG. 10 (FIG. 10(b) shows a cross-sectional view alongline BB′ in FIG. 10(a)), a dielectric layer (for example, nitride with athickness of about 5-30 nm) may be formed on the isolation layer. Aportion of the dielectric layer 1020-1 above the n-type well 1000-1 maybe covered with photoresist, and a portion of the dielectric layer abovethe p-type well 1000-2 may be patterned to form a spacer 1020-2. Thenthe photoresist is removed. There are various approaches for formingsuch a spacer, and details thereof will be omitted here.

Because the portion of the dielectric layer 1020-1 is relatively thin, asurface thereof may have substantially the same profile as that of theunderlying structure. However, for convenience, the surface profile ofthe portion of the dielectric layer 1020-1 is not shown in FIG. 10(a).

The spacer 1020-2 includes substantially no portion formed on side wallsof the fins when the trenches between the fins have a tapered shapenarrowed from top down (it is generally the case due to characteristicsof the etching).

Next, as shown in FIG. 11 (FIG. 11(b) shows a cross-sectional view alongline BB′ in FIG. 11(a), and FIG. 11(c) shows a cross-sectional viewalong line CC′ in FIG. 11(a)), exposed portions of the sacrificial gatedielectric layer 1016 may be removed selectively (by, for example, RIE).In a case where both the sacrificial gate dielectric layer 1016 and theisolation layer 1014 comprise oxide, the RIE of the sacrificial gatedielectric layer 1016 has substantially no influence on the isolationlayer 1014, because the sacrificial gate dielectric layer 1016 isrelatively thin. The process is not needed if the sacrificial gatedielectric layer has been further patterned with the sacrificial gateconductor layer as a mask in forming the sacrificial gate stack asdescribed above.

Next, portions of the second semiconductor layer 1004 exposed due to theremoval of the sacrificial gate dielectric layer 1016 may be selectivelyremoved (by, for example, RIE). Due to the existence of the sacrificialgate stack (including the sacrificial gate dielectric layer, thesacrificial gate conductor, and the spacer), the second semiconductorlayer 1004 may be left beneath the sacrificial gate stack. As a result,the first semiconductor layer 1002 is exposed.

Next, as shown in FIG. 12 (FIG. 12(b) shows a cross-sectional view alongline BB′ in FIG. 12(a), and FIG. 12(c) shows a cross-sectional viewalong line CC′ in FIG. 12(a)), the first semiconductor layer 1002 (forexample, SiGe) may be selectively etched with respect to the secondsemiconductor layer 1004 and the substrate (for example, Si), to removethe first semiconductor layer. As such, a void is formed beneath thesecond semiconductor layer 1004. In addition, an opening is left in theisolation layer, which exposes the substrate 1000 (in the example, theopening exposes the punch-through stopper 1038).

To further improve the device performances, as shown in FIG. 13 (FIG.13(b) shows a cross-sectional view along line BB′ in FIG. 13(a), andFIG. 13(c) shows a cross-sectional view along line CC′ in FIG. 13(a)),the void formed beneath the second semiconductor layer 1004 may befilled with a dielectric material, to form an isolation island 1032.Specifically, the dielectric material (for example, oxide) may bedeposited and then etched back, to expose the side walls of the fin(i.e., the second semiconductor layer 1004) (and preferably also exposethe surface of the substrate 1000). As a result, the dielectric materialis filled between the second semiconductor layer 1004 and the substrate1000 to form the isolation island 1032.

Then, a third semiconductor layer 1034 may be formed on the substrateby, for example, epitaxy, as shown in FIG. 14. Next, source/drainregions may be formed in the third semiconductor layer 1034. Due to theexistence of the isolation layer and the spacer, the third semiconductorlayer 1034 extends substantially from the side walls of the secondsemiconductor layer 1004 (specifically, the side walls on upper andlower sides in FIG. 14(a)). In an embodiment of the present disclosure,the third semiconductor layer 1034 may be doped in-situ while beinggrown. In an example, for the n-type device formed on the p-type well1000-2, n-type doping may be performed. In addition, to further improvethe performances, the third semiconductor layer 1034 may comprise amaterial different from that of the second semiconductor layer 1004, toapply stress to the second semiconductor layer 1004 (in which a channelof the device will be formed). In an example, in a case where the secondsemiconductor layer 1004 comprises Si, the third semiconductor layer1034 may comprise Si:C (wherein C may have an atomic percentage of about0.2-2%) to apply tensile stress.

As such, the second semiconductor layer 1004 together with the thirdsemiconductor layer 1034 located on opposite sides thereof constitute a“fin” for the final device. In the fin, the channel may be formed in thesecond semiconductor layer 1004 beneath the gate stack, and thesource/drain regions may be formed in the third semiconductor layer1034. In addition, the isolation island 1032 may be formed between thesource/drain regions at the bottom of the fin. The isolation island cansignificantly reduce a leakage current between the source and the drainvia the bottom of the fin.

It is to be noted that the third semiconductor layer may also includesome portions grown on the sacrificial gate conductor layer 1018 duringthe epitaxial growth if the sacrificial gate conductor layer 1018comprises polysillion. Those portions may be removed in subsequentprocesses such as a planarization process, a gate replacement process orthe like. For convenience, those portions are not shown here. Inaddition, the third semiconductor layer may be grown directly withoutforming the isolation island. As such, the second semiconductor layer1004 may also be connected to the substrate via the third semiconductorlayer at the bottom.

After the n-type device on the p-type well 1000-2 is processed asdescribed above, similar processes may be performed for the p-typedevice on the n-type well 1000-1.

Specifically, as shown in FIG. 15, a further dielectric layer 1036 (forexample, oxide) may be deposited, and then planarized by, for example,CMP, to expose the portion of the dielectric layer 1020-1 on the n-typewell 1000-1. Then, RIE may be applied on the portion of the dielectriclayer 1020-1 to form a spacer 1020-1.

Operations as described above in conjunction with FIGS. 11-14 may beperformed on the p-type device on the n-type well 1000-1, with anexception that a further third semiconductor layer 1042 may be dopedinto p-type in situ and may comprise SiGe (wherein Ge may have an atomicpercentage of about 15-75% for example) to apply compressive stress.

As shown in FIG. 15(c), for the p type device, the fin similarlyincludes the second semiconductor layer 1004 as well as the furtherthird semiconductor layer 1042 located on opposite sides thereof. In thefin, a channel may be formed in the second semiconductor layer 1004beneath the gate stack, and source/drain regions may be formed in thefurther third semiconductor layer 1042. In addition, an isolation island1040 may be formed between the source/drain regions at the bottom of thefin. The isolation island can significantly reduce a leakage currentbetween the source and the drain via the bottom of the fin.

After the source/drain regions of the n-type device and the p-typedevice are formed respectively as described above, the gate replacementprocess may be performed, to replace the sacrificial gate stack with areal gate stack for the final devices. For example, this may be done asfollows.

Next, as shown in FIG. 16 (FIG. 16 (b) shows a cross-sectional viewalong line BB′ in FIG. 16(a), and FIG. 16(c) shows a cross-sectionalview along line CC′ in FIG. 16(a)), a dielectric layer 1022 may beformed through, for example, deposition. The dielectric layer 1022 maycomprise oxide, for example. Then, the dielectric layer 1022 isplanarized by, for example, CMP, which may stop at the spacers 1020-1and 1020-2, thereby exposing the sacrificial gate conductor layer 1018.

Subsequently, as shown in FIG. 17 (FIG. 17(b) shows a cross-sectionalview along line BB′ in FIG. 17(a), and FIG. 17(c) shows across-sectional view along line CC′ in FIG. 17(a)), the sacrificial gateconductor layer 1018 may be selectively removed by, for example, a TMAHsolution, and thus voids 1024 are formed within the respective spacers1020-1 and 1020-2. In another example, the sacrificial gate dielectriclayer 1016 may be further removed.

Next, as shown in FIG. 18 (FIG. 18(b) shows a cross-sectional view alongline BB′ in FIG. 18(a), and FIG. 18(c) shows a cross-sectional viewalong line CC′ in FIG. 18(a)), a final gate stack is formed by forming agate dielectric layer 1026 and a gate conductor layer 1028 in each ofthe voids 1024. The gate dielectric layer 1026 may comprise a high-Kgate dielectric, such as HfO₂, with a thickness of about 1-5 nm. Thegate conductor layer 1028 may comprise a metal gate conductor. Further,a work function adjustment layer (not shown) may be formed between thegate dielectric layer 1022 and the gate conductor layer 1024.

Although the gate dielectric layer 1026 is shown in FIG. 18 as a thinlayer at the bottom of the void 1024, the gate dielectric layer 1026 maybe also formed on sidewalls of the void 1024 and thus surrounds the gateconductor layer 1028.

As shown in FIG. 18, the semiconductor device according to theembodiment of the present disclosure may comprise the fin formed on thesubstrate. The punch-through stopper 1038 may be formed in the substratebeneath the fin. The fin may include a portion composed of the secondsemiconductor layer 1004 beneath the gate stack and also a portioncomposed of the third semiconductor layer 1034 or 1042 abutting thesecond semiconductor layer. The semiconductor device may furthercomprise the source/drain regions formed in the portion composed of thethird semiconductor layer, the isolation layer formed on thesemiconductor substrate, and the gate stack crossing over the fin formedon the isolation layer. The isolation island 1032 may be interposedbetween the portion composed of the second semiconductor layer 1004 andthe substrate.

In case of the complementary process as described in the example, then-type and p-type devices are processed respectively. To do this, thep-type device region on the left side is shielded by the dielectriclayer portion 1020-1 to expose the n-type device region on the rightside. However, the present disclosure is not limited thereto. Forexample, in the non-complementary process, such shielding may beomitted.

In addition, in the example, the p-type device region is firstlyshielded and then the n-type device region is processed. However, thepresent disclosure is not limited thereto. An order in which the n-typedevice region and the p-type device region are processed may beexchanged.

In addition, in the above example, the gate replacement process isdescribed. However, the present disclosure is not limited thereto. Forexample, the present disclosure is also applicable to a gate-firstprocess.

In the above descriptions, details of patterning and etching of thelayers are not described. It is to be understood by those skilled in theart that various measures may be utilized to form the layers and regionsin desired shapes. Further, to achieve the same feature, those skilledin the art can devise processes not entirely the same as those describedabove. The mere fact that the various embodiments are describedseparately does not mean that means recited in the respectiveembodiments cannot be used in combination to advantage.

The present disclosure is described above with reference to theembodiments thereof. However, those embodiments are provided just forillustrative purpose, rather than limiting the present disclosure. Thescope of the disclosure is defined by the attached claims as well asequivalents thereof. Those skilled in the art can make variousalternations and modifications without departing from the scope of thedisclosure, which all fall within the scope of the disclosure.

We claim:
 1. A method for manufacturing a semiconductor device, comprising: forming a first semiconductor layer and a second semiconductor layer sequentially on a substrate; patterning the second semiconductor layer and the first semiconductor layer to form a fin; forming an isolation layer on the substrate, wherein the isolation layer exposes a portion of the first semiconductor layer; implanting ions into a portion of the substrate beneath the fin, to form a punch-through stopper; forming a gate stack crossing over the fin on the isolation layer; selectively etching the second semiconductor layer with the gate stack as a mask, to expose the first semiconductor layer; selectively etching the first semiconductor layer, to form a void beneath the second semiconductor layer; and forming a third semiconductor layer on the substrate, to form source/drain regions.
 2. The method according to claim 1, wherein after selectively etching the first semiconductor layer, the method further comprises: filling the void with a dielectric material.
 3. The method according to claim 1, wherein forming an isolation layer comprises: depositing on the substrate a dielectric material substantially covering the fin, wherein a portion of the dielectric material on top of the fin has a thickness sufficiently less than that of a portion of the dielectric material on the substrate; and etching back the dielectric material.
 4. The method according to claim 3, wherein the portion of the dielectric material on top of the fin has a thickness less than ⅓ of the thickness of the portion of the dielectric material on the substrate.
 5. The method according to claim 3, wherein the dielectric material is formed by High Density Plasma (HDP) deposition.
 6. The method according to claim 3, wherein a plurality of fins are formed on the substrate, and a portion of the dielectric material on top of each of the fins has a thickness less than ½ of a spacing between the fin and its neighboring fin.
 7. The method according to claim 1, wherein before patterning the fin, the method further comprises: forming a protection layer on the second semiconductor layer.
 8. The method according to claim 3, wherein before patterning the fin, the method further comprises: forming a protection layer on the second semiconductor layer, wherein the protection layer comprises the same dielectric material as the isolation layer.
 9. The method according to claim 1, wherein forming a punch-through stopper comprises: performing n-type implantation for a p-type device, or performing p-type implantation for an n-type device.
 10. The method according to claim 1, wherein the third semiconductor layer is doped in situ while being formed.
 11. The method according to claim 1, wherein the third semiconductor layer is compressive stressed for a p-type device or tensile stressed for an n-type device.
 12. The method according to claim 11, wherein the substrate comprises Si, the first semiconductor layer comprises SiGe, the second semiconductor layer comprises Si, and the third semiconductor layer comprises SiGe or Si:C.
 13. The method according to claim 1, wherein the gate stack is a sacrificial gate stack, and the method further comprises removing the sacrificial gate stack and forming a further gate stack by a gate replacement process.
 14. A semiconductor device, comprising: a fin formed on a substrate; a punch-through stopper formed in the substrate beneath the fin; an isolation layer formed on the substrate; and a gate stack formed on the isolation layer and crossing over the fin, wherein the fin comprises a portion composed of a first semiconductor layer beneath the gate stack and a portion composed of a second semiconductor layer abutting the first semiconductor layer, and wherein the semiconductor device further comprises source/drain regions formed in the portion composed of the second semiconductor layer and the isolation layer has a top surface lower than a bottom surface of the portion composed of the first semiconductor layer.
 15. The semiconductor device according to claim 14, further comprising an isolation island formed between the portion composed of the first semiconductor layer and the substrate.
 16. The semiconductor device according to claim 14, wherein the substrate comprises Si, the first semiconductor layer comprises Si, and the second semiconductor layer comprises SiGe or Si:C.
 17. The semiconductor device according to claim 14, wherein the portion composed of the second semiconductor layer is formed on a surface of the substrate through an opening in the isolation layer.
 18. A semiconductor device, comprising: a fin formed on a substrate; a punch-through stopper formed in the substrate beneath the fin; an isolation layer formed on the substrate; and a gate stack formed on the isolation layer and crossing over the fin, wherein the fin comprises a portion of a first semiconductor layer beneath the gate stack and a portion composed of a second semiconductor layer abutting the first semiconductor layer, and an isolation island formed between the portion composed of the first semiconductor layer and the substrate; wherein the semiconductor device further comprises source/drain regions formed in the portion composed of the second semiconductor layer.
 19. The semiconductor device according to claim 18, wherein the isolation layer has a top surface lower than a bottom surface of the portion composed of the first semiconductor layer.
 20. The semiconductor device according to claim 18, wherein the substrate comprises Si, the first semiconductor layer comprises Si, and the second semiconductor layer comprises SiGe or Si:C. 